# Draft California 2012 Integrated Report( 303(d) List/305(b) Report)

# Supporting Information

## Regional Board 6 - Lahontan Region

Water Body Name: | Mill Creek (Modoc County)
Water Body ID: | CAR6413001119980804160434
Water Body Type: | River & Stream

DECISION ID | 21083 | Region 6
Mill Creek (Modoc County)

Pollutant: | Chloride
Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)(2010)
Revision Status | Original
Impairment from Pollutant or Pollution: | Pollutant
Regional Board Staff Conclusion: | Regional Board Conclusion: This pollutant was considered for placement on the section 303(d) list in a previous assessment cycle. No new information was reviewed for this current assessment cycle. Therefore, the previous conclusion remains unchanged, and is as follows: This pollutant is being considered for placement on the section 303(d) list under section 3.2 of the Listing Policy. Under section 3.2 a single line of evidence is necessary to assess listing status. Two lines of evidence are available in the administrative record to assess this pollutant. None of the individual samples exceed the California Maximum Contaminant Level for chloride. None of the annual average datapoints exceed the site-specific water quality objective. Based on the readily available data and information, the weight of evidence indicates that there is sufficient justification against placing this water segment-pollutant combination on the section 303(d) list in the Water Quality Limited Segments category. This conclusion is based on the staff findings that: 1. The data used satisfy the data quality requirements of section 6.1.4 of the Policy. 2. The data used do not satisfy the data quantity requirements of section 6.1.5 of the Policy. Quarterly samples do not capture the seasonal and annual variability expected in streamflows and constituent concentrations in streams of the Lahontan Region. 3. None of the 14 individual samples or five annual average datapoints exceeded the applicable water quality objectives and this does not exceed the allowable frequency listed in Table 3.2 of the Listing Policy. 4. Pursuant to section 3.11 of the Listing Policy, no additional data and information are available indicating that standards are not met.
Regional Board Staff Decision Recommendation: | No new data were assessed for this assessment cycle. The conclusion reached in the previous cycle remains in same. The Regional Board will update this decision when new data and information become available in a future assessment cycle.

Line of Evidence (LOE) for Decision ID 21083, Chloride | Region 6
Mill Creek (Modoc County)
LOE ID: | 4839
Pollutant: | Chloride
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | Dissolved
Beneficial Use: | Cold Freshwater Habitat
Number of Samples: | 5
Number of Exceedances: | 0
Data and Information Type: | Non-fixed station physical/chemical monitoring (conventional pollutant only)
Data Used to Assess Water Quality: | The U.S. Geological Survey collected chloride data for Mill Creek under the Region 6 SWAMP program. Fourteen samples were collected over 5 years between 2001 and 2005 (2 to 4 samples/year). Chloride concentrations ranged from less than the detection level to 2.05 mg/L. There was one estimated value. The annual average objective was not exceeded.
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | The site-specific objective for chloride in Lahontan Basin Plan Table 3-7 is 1 mg/L as an annual average.
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | Fourteen samples were collected over a 5 year period between 2001 and 2005, with 2-4 samples per year. Five annual average calculations were done.
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest. Chloride concentrations in the lower reach of the creek may be influenced by windblown salts from the dry lake bed.
QAPP Information: | The data meet the quality assurance requirements of the SWAMP QAPP.
QAPP Information Reference(s):
Line of Evidence (LOE) for Decision ID 21083, Chloride | Region 6
Mill Creek (Modoc County)
LOE ID: | 4840
Pollutant: | Chloride
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | Dissolved
Beneficial Use: | Municipal & Domestic Supply
Number of Samples: | 14
Number of Exceedances: | 0
Data and Information Type: | Fixed station physical/chemical (conventional plus toxic pollutants)
Data Used to Assess Water Quality: | The U.S. Geological Survey collected chloride data for Mill Creek under the Region 6 SWAMP program. Fourteen samples were collected over 5 years between 2001 and 2005 (2 to 4 samples/year). Chloride concentrations ranged from less than the detection level to 2.05 mg/L. There was one estimated value. The MCL was not exceeded.
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | California Maximum Contaminant Levels (MCLs) apply to ambient waters under the Lahontan Basin Plan's "Chemical Constituents" objective. The MCL for chloride is 250 mg/L.
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | Fourteen samples were collected over a 5 year period between 2001 and 2005, with 2-4 samples per year.
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest. Chloride concentrations in the lower reach of the creek may be influenced by windblown salts from the dry lake bed.
QAPP Information: | The data meet the quality assurance requirements of the SWAMP QAPP.
QAPP Information Reference(s):

DECISION ID | 21816 | Region 6
Mill Creek (Modoc County)

Pollutant: | Dissolved oxygen saturation
Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)(2010)
Revision Status | Original
Impairment from Pollutant or Pollution: | Pollutant
Regional Board Staff Conclusion: | Regional Board Conclusion: This pollutant was considered for placement on the section 303(d) list in a previous assessment cycle. No new information was reviewed for this current assessment cycle. Therefore, the previous conclusion remains unchanged, and is as follows: This pollutant is being considered for placement on the section 303(d) list under section 3.2 of the Listing Policy. Under section 3.2 a single line of evidence is necessary to assess listing status. One line of evidence is available in the administrative record to assess this pollutant. One of the samples exceeds the water quality objective. Based on the readily available data and information, the weight of evidence indicates that there is sufficient justification against placing this water segment-pollutant combination on the section 303(d) list in the Water Quality Limited Segments category. This conclusion is based on the staff findings that: 1. The data used satisfy the data quality requirements of section 6.1.4 of the Policy. 2. The data used do not satisfy the data quantity requirements of section 6.1.5 of the Policy. 3. One of two samples exceeded the water quality objective and this does not exceed the allowable frequency listed in Table 3.2 of the Listing Policy. 4. Pursuant to section 3.11 of the Listing Policy, no additional data and information are available indicating that standards are not met.
Regional Board Staff Decision Recommendation: | No new data were assessed for this assessment cycle. The conclusion reached in the previous cycle remains in same. The Regional Board will update this decision when new data and information become available in a future assessment cycle.

Line of Evidence (LOE) for Decision ID 21816, Dissolved oxygen saturation | Region 6
Mill Creek (Modoc County)
LOE ID: | 5725
Pollutant: | Dissolved oxygen saturation
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | Dissolved
Beneficial Use: | Cold Freshwater Habitat
Number of Samples: | 2
Number of Exceedances: | 1
Data and Information Type: | Fixed station physical/chemical (conventional plus toxic pollutants)
Data Used to Assess Water Quality: | The U.S. Geological Survey sampled Mill Creek under the Region 6 SWAMP program. Two measurements of dissolved oxygen as percent saturation were taken in October 2004 and July 2005. Percent saturation values were 101 and 72 percent. One sample violated the 80 percent minimum in the objective.
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | The Lahontan Basin Plan's regionwide narrative objective for dissolved oxygen provides that percent saturation shall not be depressed more than 10 percent nor shall the minimum dissolved oxygen concentration be less than 80 percent of saturation.
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | Two samples were collected in October 2004 and July 2005. This sampling frequency was inadequate to characterize natural diel, seasonal, and annual variation in dissolved oxygen concentration.
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest. In addition to the Cold Freshwater Habitat beneficial use, Mill Creek is designated for the Spawning, Reproduction and Development use.
QAPP Information: | The data meet the quality assurance requirements of the SWAMP QAPP.
QAPP Information Reference(s):

DECISION ID | 20930 | Region 6
Mill Creek (Modoc County)

Pollutant: | Fecal Coliform
Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)(2010)
Revision Status | Original
Impairment from Pollutant or Pollution: | Pollutant
Regional Board Staff Conclusion: | Regional Board Conclusion: This pollutant was considered for placement on the section 303(d) list in a previous assessment cycle. No new information was reviewed for this current assessment cycle. Therefore, the previous conclusion remains unchanged, and is as follows: This pollutant is being considered for placement on the section 303(d) list under section 3.3 of the Listing Policy. Under section 3.3 a single line of evidence is necessary to assess listing status. Two lines of evidence are available in the administrative record to assess this pollutant. Two of the samples exceed the water quality objective. Based on the readily available data and information, the weight of evidence indicates that there is sufficient justification against placing this water segment-pollutant combination on the section 303(d) list in the Water Quality Limited Segments category. This conclusion is based on the staff findings that: 1. The data used satisfy the data quality requirements of section 6.1.4 of the Policy. 2. The data used do not satisfy the data quantity requirements of section 6.1.5 of the Policy. Quarterly samples do not capture the seasonal and annual variability expected in streamflows and fecal coliform counts in streams of the Lahontan Region. The water quality objective calls for collection of five samples within a 30-day period. 3. Two of seven samples exceeded the water quality objective and this does not exceed the allowable frequency listed in Table 3.2 of the Listing Policy. 4. Pursuant to section 3.11 of the Listing Policy, no additional data and information are available indicating that standards are not met.
Regional Board Staff Decision Recommendation: | No new data were assessed for this assessment cycle. The conclusion reached in the previous cycle remains in same. The Regional Board will update this decision when new data and information become available in a future assessment cycle.

Line of Evidence (LOE) for Decision ID 20930, Fecal Coliform | Region 6
Mill Creek (Modoc County)
LOE ID: | 5692
Pollutant: | Fecal Coliform
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | None
Beneficial Use: | Municipal & Domestic Supply
Number of Samples: | 7
Number of Exceedances: | 2
Data and Information Type: | Water column surveys (e.g. fecal coliform)
Data Used to Assess Water Quality: | The U.S. Geological Survey sampled Mill Creek under the Region 6 SWAMP program between 2003 and 2005. The fecal coliform counts in four of seven samples were estiimated values, and one sample was below the detection level. The remaining two samples with counts of 68 and 220 colonies per 100 mL, exceeded the limits in the objective.
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | The Lahontan Basin Plan's objective for coliform bacteria states: "Waters shall not contain concentrations of coliform organisms attributable to anthropogenic sources, including human and livestock waste. The fecal coliform concentration during any 30-day period shall not exceed a log mean of 20/100 ml, nor shall more than 10 percent of all samples collected during any 30-day period exceed 40/100 ml. The log mean shall ideally be based on a minimum of not less than five samples collected a evenly spaced as practicable during any 30-day period. However, a log mean concentration exceeding 20/100 ml for any 30-day period shall indicate violation of this objective even if fewer than five samples were collected."
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | Seven samples were collected at quarterly intervals (2-3 samples per year) between 2003 and 2005.
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest.
QAPP Information: | The data meet the quality assurance requirements of the SWAMP QAPP.
QAPP Information Reference(s):
Line of Evidence (LOE) for Decision ID 20930, Fecal Coliform | Region 6
Mill Creek (Modoc County)
LOE ID: | 5693
Pollutant: | Fecal Coliform
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | None
Beneficial Use: | Water Contact Recreation
Number of Samples: | 7
Number of Exceedances: | 2
Data and Information Type: | Water column surveys (e.g. fecal coliform)
Data Used to Assess Water Quality: | The U.S. Geological Survey sampled Mill Creek under the Region 6 SWAMP program between 2003 and 2005. The fecal coliform counts in four of seven samples were estiimated values, and one sample was below the detection level. The remaining two samples with counts of 68 and 220 colonies per 100 mL, exceeded the limits in the objective.
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | The Lahontan Basin Plan's objective for coliform bacteria states: "Waters shall not contain concentrations of coliform organisms attributable to anthropogenic sources, including human and livestock waste. The fecal coliform concentration during any 30-day period shall not exceed a log mean of 20/100 ml, nor shall more than 10 percent of all samples collected during any 30-day period exceed 40/100 ml. The log mean shall ideally be based on a minimum of not less than five samples collected a evenly spaced as practicable during any 30-day period. However, a log mean concentration exceeding 20/100 ml for any 30-day period shall indicate violation of this objective even if fewer than five samples were collected."
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | Seven samples were collected at quarterly intervals (2-3 samples per year) between 2003 and 2005.
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest.
QAPP Information: | The data meet the quality assurance requirements of the SWAMP QAPP.
QAPP Information Reference(s):

DECISION ID | 21960 | Region 6
Mill Creek (Modoc County)

Pollutant: | Nitrate
Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)(2010)
Revision Status | Original
Impairment from Pollutant or Pollution: | Pollutant
Regional Board Staff Conclusion: | Regional Board Conclusion: This pollutant was considered for placement on the section 303(d) list in a previous assessment cycle. No new information was reviewed for this current assessment cycle. Therefore, the previous conclusion remains unchanged, and is as follows: This pollutant is being considered for placement on the section 303(d) list under section 3.1 of the Listing Policy. Under section 3.1 a single line of evidence is necessary to assess listing status. One line of evidence is available in the administrative record to assess this pollutant. None of the samples exceed the water quality objective. Based on the readily available data and information, the weight of evidence indicates that there is sufficient justification against placing this water segment-pollutant combination on the section 303(d) list in the Water Quality Limited Segments category. This conclusion is based on the staff findings that: 1. The data used satisfy the data quality requirements of section 6.1.4 of the Policy. 2. The data used do not satisfy the data quantity requirements of section 6.1.5 of the Policy. Quarterly samples do not capture the seasonal and annual variability expected in streamflows and constituent concentrations in streams of the Lahontan Region. 3. None of 10 samples exceeded the Maximum Contaminant Level and this does not exceed the allowable frequency listed in Table 3.1 of the Listing Policy. 4. Pursuant to section 3.11 of the Listing Policy, no additional data and information are available indicating that standards are not met.
Regional Board Staff Decision Recommendation: | No new data were assessed for this assessment cycle. The conclusion reached in the previous cycle remains in same. The Regional Board will update this decision when new data and information become available in a future assessment cycle.

Line of Evidence (LOE) for Decision ID 21960, Nitrate | Region 6
Mill Creek (Modoc County)
LOE ID: | 7481
Pollutant: | Nitrate
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | Dissolved
Beneficial Use: | Municipal & Domestic Supply
Number of Samples: | 10
Number of Exceedances: | 0
Data and Information Type: | Fixed station physical/chemical (conventional plus toxic pollutants)
Data Used to Assess Water Quality: | The U.S. Geological Survey sampled Mill Creek under the Region 6 SWAMP program. Ten quarterly samples for nitrite plus nitrate (as N) were collected between 2002 and 2005 (1 to 4 samples/year). Concentrations in three samples were below the detection level. Concentrations in the remaining samples ranged from 0.001 to 0.087 mg/L. The combined concentration of nitrite plus nitrate did not exceed the MCL for nitrate.
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | California Maximum Contaminant Levels (MCLs) apply to ambient waters under the Lahontan Basin Plan's "Chemical Constituents" objective. The MCL for nitrate is 45 mg/L expressed "as nitrate", equivalent to 10 mg/L expressed "as N."
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | Ten samples were collected at quarterly intervals between 2002 and 2005, with 1 to 4 samples per year.
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest. Chloride concentrations in the lower reach of the creek may be influenced by windblown salts from the dry lake bed.
QAPP Information: | The data meet the quality assurance requirements of the SWAMP QAPP.
QAPP Information Reference(s):

DECISION ID | 21856 | Region 6
Mill Creek (Modoc County)

Pollutant: | Nitrate/Nitrite (Nitrite + Nitrate as N)
Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)(2010)
Revision Status | Original
Impairment from Pollutant or Pollution: | Pollutant
Regional Board Staff Conclusion: | Regional Board Conclusion: This pollutant was considered for placement on the section 303(d) list in a previous assessment cycle. No new information was reviewed for this current assessment cycle. Therefore, the previous conclusion remains unchanged, and is as follows: This pollutant is being considered for placement on the section 303(d) list under section 3.1 of the Listing Policy. Under section 3.1 a single line of evidence is necessary to assess listing status. Two lines of evidence are available in the administrative record to assess this pollutant. None of the samples exceed the Maximum Contaminant Level. No biological data are available to detemine whether the data exceed the objective for biostimulatory substances. Based on the readily available data and information, the weight of evidence indicates that there is sufficient justification against placing this water segment-pollutant combination on the section 303(d) list in the Water Quality Limited Segments category. This conclusion is based on the staff findings that: 1. The data used satisfy the data quality requirements of section 6.1.4 of the Policy. 2. The data used do not satisfy the data quantity requirements of section 6.1.5 of the Policy. Quarterly samples do not capture the seasonal and annual variability expected in streamflows and constituent concentrations in streams of the Lahontan Region. 3. None of 10 samples exceeded the Maximum Contaminant Level and this does not exceed the allowable frequency listed in Table 3.1 of the Listing Policy. There is no available biological information for assessment of compliance with the objective for biostimulatory substances. 4. Pursuant to section 3.11 of the Listing Policy, no additional data and information are available indicating that standards are not met.
Regional Board Staff Decision Recommendation: | No new data were assessed for this assessment cycle. The conclusion reached in the previous cycle remains in same. The Regional Board will update this decision when new data and information become available in a future assessment cycle.

Line of Evidence (LOE) for Decision ID 21856, Nitrate/Nitrite (Nitrite + Nitrate as N) | Region 6
Mill Creek (Modoc County)
LOE ID: | 5812
Pollutant: | Nitrate/Nitrite (Nitrite + Nitrate as N)
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | Dissolved
Beneficial Use: | Cold Freshwater Habitat
Number of Samples: | 10
Number of Exceedances: | 0
Data and Information Type: | Fixed station physical/chemical (conventional plus toxic pollutants)
Data Used to Assess Water Quality: | The U.S. Geological Survey sampled Mill Creek under the Region 6 SWAMP program. Ten quarterly samples were collected between 2002 and 2005 (1 to 4 samples/year). Concentrations of nitrate plus nitrite in three samples were below the detection level. Concentrations in the remaining samples ranged from 0.001 to 0.087 mg/L. No data on algae or macrophytes are available for assessment of compliance with the water quality objective for biostimulatory substances.
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | The Lahontan Basin Plan does not include site-specific objectives for nitrate, nitrite, or nitrate plus nitrite for Mill Creek. A separate LOE has been prepared for the Total Nitrogen objective in Basin Plan Table 3-7. The narrative objective for biostimulatory substances states: "Waters shall not contain biostimulatory substances in concentrations that promote aquatic growths to the extent that such growths cause nuisance or adversely affect the water for beneficial uses."
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | Ten samples were collected at quarterly intervals between 2002 and 2005, with 1 to 4 samples per year.
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest. Chloride concentrations in the lower reach of the creek may be influenced by windblown salts from the dry lake bed.
QAPP Information: | The data meet the quality assurance requirements of the SWAMP QAPP.
QAPP Information Reference(s):
Line of Evidence (LOE) for Decision ID 21856, Nitrate/Nitrite (Nitrite + Nitrate as N) | Region 6
Mill Creek (Modoc County)
LOE ID: | 7594
Pollutant: | Nitrate/Nitrite (Nitrite + Nitrate as N)
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | Dissolved
Beneficial Use: | Municipal & Domestic Supply
Number of Samples: | 10
Number of Exceedances: | 0
Data and Information Type: | Fixed station physical/chemical (conventional plus toxic pollutants)
Data Used to Assess Water Quality: | The U.S. Geological Survey sampled Mill Creek under the Region 6 SWAMP program. Ten quarterly samples were collected between 2002 and 2005 (1 to 4 samples/year). Concentrations of nitrate plus nitrite in three samples were below the detection level. Concentrations in the remaining samples ranged from 0.001 to 0.087 mg/L. The MCL was not exceeded.
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | California Maximum Contaminant Levels (MCLs) apply to ambient waters under the Lahontan Basin Plan's "Chemical Constituents" objective. The MCL for nitrite plus nitrate expressed "as N" is 10 mg/L.
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | Ten samples were collected at quarterly intervals between 2002 and 2005, with 1 to 4 samples per year.
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest. Chloride concentrations in the lower reach of the creek may be influenced by windblown salts from the dry lake bed.
QAPP Information: | The data meet the quality assurance requirements of the SWAMP QAPP.
QAPP Information Reference(s):

DECISION ID | 21815 | Region 6
Mill Creek (Modoc County)

Pollutant: | Nitrite
Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)(2010)
Revision Status | Original
Impairment from Pollutant or Pollution: | Pollutant
Regional Board Staff Conclusion: | Regional Board Conclusion: This pollutant was considered for placement on the section 303(d) list in a previous assessment cycle. No new information was reviewed for this current assessment cycle. Therefore, the previous conclusion remains unchanged, and is as follows: This pollutant is being considered for placement on the section 303(d) list under section 3.1 of the Listing Policy. Under section 3.1 a single line of evidence is necessary to assess listing status. One line of evidence is available in the administrative record to assess this pollutant. None of the samples exceed the water quality objective. Based on the readily available data and information, the weight of evidence indicates that there is sufficient justification against placing this water segment-pollutant combination on the section 303(d) list in the Water Quality Limited Segments category. This conclusion is based on the staff findings that: 1. The data used satisfy the data quality requirements of section 6.1.4 of the Policy. 2. The data used do not satisfy the data quantity requirements of section 6.1.5 of the Policy. Quarterly samples do not capture the seasonal and annual variability expected in streamflows and constituent concentrations in streams of the Lahontan Region. 3. None of 10 samples exceeded the water quality objective and this does not exceed the allowable frequency listed in Table 3.1 of the Listing Policy. 4. Pursuant to section 3.11 of the Listing Policy, no additional data and information are available indicating that standards are not met.
Regional Board Staff Decision Recommendation: | No new data were assessed for this assessment cycle. The conclusion reached in the previous cycle remains in same. The Regional Board will update this decision when new data and information become available in a future assessment cycle.

Line of Evidence (LOE) for Decision ID 21815, Nitrite | Region 6
Mill Creek (Modoc County)
LOE ID: | 7482
Pollutant: | Nitrite
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | Dissolved
Beneficial Use: | Municipal & Domestic Supply
Number of Samples: | 10
Number of Exceedances: | 0
Data and Information Type: | Fixed station physical/chemical (conventional plus toxic pollutants)
Data Used to Assess Water Quality: | The U.S. Geological Survey sampled Mill Creek under the Region 6 SWAMP program. Ten quarterly samples for nitrite plus nitrate (as N) were collected between 2002 and 2005 (1 to 4 samples/year). Concentrations in three samples were below the detection level. Concentrations in the remaining samples ranged from 0.001 to 0.087 mg/L. The combined concentration of nitrite plus nitrate did not exceed the MCL for nitrite.
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | California Maximum Contaminant Levels (MCLs) apply to ambient waters under the Lahontan Basin Plan's "Chemical Constituents" objective. The MCL for nitrite is 1 mg/L.
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | Ten samples were collected at quarterly intervals between 2002 and 2005, with 1 to 4 samples per year.
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest. Chloride concentrations in the lower reach of the creek may be influenced by windblown salts from the dry lake bed.
QAPP Information: | The data meet the quality assurance requirements of the SWAMP QAPP.
QAPP Information Reference(s):

DECISION ID | 20953 | Region 6
Mill Creek (Modoc County)

Pollutant: | Oxygen, Dissolved
Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)(2010)
Revision Status | Original
Impairment from Pollutant or Pollution: | Pollutant
Regional Board Staff Conclusion: | Regional Board Conclusion: This pollutant was considered for placement on the section 303(d) list in a previous assessment cycle. No new information was reviewed for this current assessment cycle. Therefore, the previous conclusion remains unchanged, and is as follows: This pollutant is being considered for placement on the section 303(d) list under section 3.2 of the Listing Policy. Under section 3.2 a single line of evidence is necessary to assess listing status. One line of evidence is available in the administrative record to assess this pollutant. One of the samples exceed the water quality objective. Based on the readily available data and information, the weight of evidence indicates that there is sufficient justification against placing this water segment-pollutant combination on the section 303(d) list in the Water Quality Limited Segments category. This conclusion is based on the staff findings that: 1. The data used satisfy the data quality requirements of section 6.1.4 of the Policy. 2. The data used do not satisfy the data quantity requirements of section 6.1.5 of the Policy. Quarterly samples do not capture the seasonal and annual variability expected in streamflows and constituent concentrations in streams of the Lahontan Region. 3. One of eleven samples exceeded the water quality objective and this does not exceed the allowable frequency listed in Table 3.2 of the Listing Policy. 4. Pursuant to section 3.11 of the Listing Policy, no additional data and information are available indicating that standards are not met.
Regional Board Staff Decision Recommendation: | No new data were assessed for this assessment cycle. The conclusion reached in the previous cycle remains in same. The Regional Board will update this decision when new data and information become available in a future assessment cycle.

Line of Evidence (LOE) for Decision ID 20953, Oxygen, Dissolved | Region 6
Mill Creek (Modoc County)
LOE ID: | 4841
Pollutant: | Oxygen, Dissolved
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | Dissolved
Beneficial Use: | Cold Freshwater Habitat
Number of Samples: | 11
Number of Exceedances: | 1
Data and Information Type: | Non-fixed station physical/chemical monitoring (conventional pollutant only)
Data Used to Assess Water Quality: | The U.S. Geological Survey collected dissolved oxygen data for Mill Creek under the Region 6 SWAMP program. Eleven samples were collected over 5 years between 2001 and 2005 (2 to 4 samples/year). One sample violated the objective (at 6.3 mg/L).
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | The objective (from Lahontan Basin Plan Table 3-6) is a one-day minimum dissolved oxygen concentration of 8 mg/L.
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | Eleven samples were collected over a 5 year period between 2001 and 2005, with 2-4 samples per year. This sampling frequency was inadequate to characterize natural diel, seasonal, and annual variation in dissolved oxgen concentration.
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest. In addition to the Cold Freshwater Habitat beneficial use, Mill Creek is designated for the Spawning, Reproduction and Development use.
QAPP Information: | The data meet the quality assurance requirements of the SWAMP QAPP.
QAPP Information Reference(s):

DECISION ID | 22040 | Region 6
Mill Creek (Modoc County)

Pollutant: | Phosphate
Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)(2010)
Revision Status | Original
Impairment from Pollutant or Pollution: | Pollutant
Regional Board Staff Conclusion: | Regional Board Conclusion: This pollutant was considered for placement on the section 303(d) list in a previous assessment cycle. No new information was reviewed for this current assessment cycle. Therefore, the previous conclusion remains unchanged, and is as follows: This pollutant is being considered for placement on the section 303(d) list under section 3.1 of the Listing Policy. Under section 3.1 a single line of evidence is necessary to assess listing status. One line of evidence, consisting of a single sample, is available in the administrative record to assess this pollutant. There is no associated biological evidence to determine whether the sample exceeds the water quality objective for biostimulatory substances. Based on the readily available data and information, the weight of evidence indicates that there is sufficient justification against placing this water segment-pollutant combination on the section 303(d) list in the Water Quality Limited Segments category. This conclusion is based on the staff findings that: 1. The data used satisfy the data quality requirements of section 6.1.4 of the Policy. 2. The single sample used does not satisfy the data quantity requirements of section 6.1.5 of the Policy. 3. There is insufficient evidence to determine whether the single sample exceeds the biostimulatory substances objective, and the minimum sample number requirements of Table 3.1 of the policy are not met. 4. Pursuant to section 3.11 of the Listing Policy, no additional data and information are available indicating that standards are not met.
Regional Board Staff Decision Recommendation: | No new data were assessed for this assessment cycle. The conclusion reached in the previous cycle remains in same. The Regional Board will update this decision when new data and information become available in a future assessment cycle.

Line of Evidence (LOE) for Decision ID 22040, Phosphate | Region 6
Mill Creek (Modoc County)
LOE ID: | 5810
Pollutant: | Phosphate
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | Dissolved
Beneficial Use: | Cold Freshwater Habitat
Number of Samples: | 1
Number of Exceedances: | 0
Data and Information Type: | Non-fixed station physical/chemical monitoring (conventional pollutant only)
Data Used to Assess Water Quality: | The U.S. Geological Survey sampled Mill Creek under Region 6's SWAMP program. One dissolved PO4 sample was collected on 3/24/04. No data on algae or macrophytes are available for assessment of compliance with the objective for biostimulatory substances.
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | There is no numerical site- specific objective for phosphorus in Mill Creek in the Lahontan Basin Plan. The narrative objective for Biostimulatory Substances states: "Waters shall not contain biostimulatory substances in concentrations that promote aquatic growths to the extent that such growths cause nuisance or adversely affect the waters for beneficial uses."
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | One sample was collected on 3/24/04.
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest.
QAPP Information: | The data meet the quality assurance requirements of the SWAMP QAPP.
QAPP Information Reference(s):

DECISION ID | 21741 | Region 6
Mill Creek (Modoc County)

Pollutant: | Phosphorus
Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)(2010)
Revision Status | Original
Impairment from Pollutant or Pollution: | Pollutant
Regional Board Staff Conclusion: | Regional Board Conclusion: This pollutant was considered for placement on the section 303(d) list in a previous assessment cycle. No new information was reviewed for this current assessment cycle. Therefore, the previous conclusion remains unchanged, and is as follows: This pollutant is being considered for placement on the section 303(d) list under section 3.1 of the Listing Policy. Under section 3.1 a single line of evidence is necessary to assess listing status. One line of evidence is available in the administrative record to assess this pollutant. There is insufficient biological evidence to determine whether the chemical samples exceed the water quality objective for biostimulatory substances. Based on the readily available data and information, the weight of evidence indicates that there is sufficient justification against placing this water segment-pollutant combination on the section 303(d) list in the Water Quality Limited Segments category. This conclusion is based on the staff findings that: 1. The data used do not satisfy the data quality requirements of section 6.1.4 of the Policy due to an error in the SWAMP QAPP regarding holding times for total phosphorus samples. 2. The data used do not satisfy the data quantity requirements of section 6.1.5 of the Policy. Quarterly samples do not capture the seasonal and annual variability expected in streamflows and constituent concentrations in streams of the Lahontan Region. 3. There is insufficient biological evidence to determine whether any of the 10 total phosphorus samples exceeded the objective for biostimulatory substances. 4. Pursuant to section 3.11 of the Listing Policy, no additional data and information are available indicating that standards are not met.
Regional Board Staff Decision Recommendation: | No new data were assessed for this assessment cycle. The conclusion reached in the previous cycle remains in same. The Regional Board will update this decision when new data and information become available in a future assessment cycle.

Line of Evidence (LOE) for Decision ID 21741, Phosphorus | Region 6
Mill Creek (Modoc County)
LOE ID: | 4844
Pollutant: | Phosphorus
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | Total
Beneficial Use: | Cold Freshwater Habitat
Number of Samples: | 10
Number of Exceedances: | 0
Data and Information Type: | Non-fixed station physical/chemical monitoring (conventional pollutant only)
Data Used to Assess Water Quality: | The U.S. Geological Survey collected phosporus samples for Mill Creek under Region 6's SWAMP program. The range of total phosphorus concentrations in 10 samples was 0.033 to 0.084 mg/L. No data on algae or macrophytes are available for assessment of compliance with the objective for biostimulatory substances.
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | There is no numerical site- specific objective for phosphorus in Mill Creek in the Lahontan Basin Plan. The narrative objective for Biostimulatory Substances states: "Waters shall not contain biostimulatory substances in concentrations that promote aquatic growths to the extent that such growths cause nuisance or adversely affect the waters for beneficial uses."
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | Ten quarterly samples were collected over a 4 year period between July 2002 and July 2005, with 1 to 4 samples per year.
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest.
QAPP Information: | Sampling and analysis were done according to the SWAMP QAPP. However, in July 2009 an error was discovered in the QAPP related to holding times for total phosphorus samples that affects the validity of data for the Lahontan Region The holding time for samples that are not acid-preserved.should be 48 hours rather than 28 days as indicated in the QAPP. "Low level" phosphorus analyses, without acid preservation, are used in the Lahontan Region's SWAMP program. .
QAPP Information Reference(s):

DECISION ID | 28230 | Region 6
Mill Creek (Modoc County)

Pollutant: | Sedimentation/Siltation
Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)(2010)
Revision Status | Original
Impairment from Pollutant or Pollution: | Pollutant
Regional Board Staff Conclusion: | Regional Board Conclusion: This pollutant was considered for placement on the section 303(d) list in a previous assessment cycle. No new information was reviewed for this current assessment cycle. Therefore, the previous conclusion remains unchanged, and is as follows: Mill Creek was delisted for sedimentation/siltation in 2006 because the original listing was based on faulty data. New sediment data are available. However, they are insufficient to determine whether or not the creek should be listed. The Lahontan Basin Plan's narrative water quality objective is an antidegradation based objective that provides that there shall be no increases in suspended sediment concentrations or loads. This pollutant is being considered for placement on the section 303(d) list under section 3.10 of the Listing Policy, which deals with trends in water quality. One line of evidence documents the basis for delisting. Another line of evidence, based on quarterly sampling, is available in the administrative record to assess this pollutant. It includes 12 suspended sediment concentration values and 12 suspended sediment load values calculated from instantaneous discharge measurements. Suspended sediment concentrations and loads are dependent on flows and can change rapidly over a short time during storm or snowmelt runoff events. Quarterly samples are insufficient to capture these short term events and therefore are insufficient to define natural background suspended sediment concentrations and loads, or to detect trends. Listing Policy Section 3.10 requires that natural background conditions be established. Based on the readily available data and information, the weight of evidence indicates that there is sufficient justification against placing this water segment-pollutant combination on the section 303(d) list in the Water Quality Limited Segments category. This conclusion is based on the staff findings that: 1. The data used satisfy the data quality requirements of section 6.1.4 of the Policy. 2. The data used do not satisfy the data quantity requirements of section 6.1.5. Quarterly samples do not capture the seasonal and annual variability expected in streamflows and constituent concentrations in streams of the Lahontan Region. 3. Sampling frequency was insufficient to establish natural background conditions and therefore does not meet the requirements of Listing Policy section 3.10. 4. Pursuant to section 3.11 of the Listing Policy, no additional data and information are available indicating that standards are not met.
Regional Board Staff Decision Recommendation: | No new data were assessed for this assessment cycle. The conclusion reached in the previous cycle remains in same. The Regional Board will update this decision when new data and information become available in a future assessment cycle.

Line of Evidence (LOE) for Decision ID 28230, Sedimentation/Siltation | Region 6
Mill Creek (Modoc County)
LOE ID: | 2874
Pollutant: | Sedimentation/Siltation
LOE Subgroup: | Testimonial Evidence
Matrix: | Not Specified
Fraction: | None
Beneficial Use: | Cold Freshwater Habitat
Number of Samples: |
Number of Exceedances: |
Data and Information Type: | Not Specified
Data Used to Assess Water Quality: | The original listing based on qualitative information in a 1980s Modoc National Forest Management Plan EIR. No data or QA/QC information was available and the listing document is no longer available to water quality assessment staff. This listing basis was faulty due to lack of data. Regional Board staff is not aware of evidence to indicate current water quality standards exceedances or beneficial use impacts related to the listing for this pollutant.
Data Reference: | Placeholder reference 2006 303(d)
SWAMP Data: | Non-SWAMP
Water Quality Objective/Criterion: |
Objective/Criterion Reference:
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: |
Temporal Representation: |
Environmental Conditions: |
QAPP Information: | QA Info Missing
QAPP Information Reference(s):
Line of Evidence (LOE) for Decision ID 28230, Sedimentation/Siltation | Region 6
Mill Creek (Modoc County)
LOE ID: | 4846
Pollutant: | Sediment
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | None
Beneficial Use: | Cold Freshwater Habitat
Number of Samples: | 12
Number of Exceedances: | 0
Data and Information Type: | Non-fixed station physical/chemical monitoring (conventional pollutant only)
Data Used to Assess Water Quality: | The U.S. Geological Survey sampled suspended sediment in Mill Creek under Region 6's SWAMP program at quarterly intervals between 2001 and 2005, and performed loading calculations using concurrent "instantaneous discharge" flow data. Fourteen instantaneous discharge measurements included one estimated value. The remainder ranged from 0.03 to 15 cubic feet per second. Suspended sediment concentrations in 12 samples ranged from below detection level to 70 mg/L. Four of eight loading calculations were less than 0.01 ton per day and the remainder ranged from 0.01 to 2.3 tons per day.
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | The Lahontan Basin Plan's narrative objective for suspended sediment states: "The suspended sediment load and suspended sediment discharge rate of surface waters shall not be altered in such a manner as to cause nuisance or adversely affect the water for beneficial uses."
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | 12 suspended sediment samples were collected over 5 years (2- 4 samples/year, between 2001 to 2005). Eight loading calculations were done.
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest.
QAPP Information: | The data meet the quality assurance requirements of the SWAMP QAPP.
QAPP Information Reference(s):

DECISION ID | 21059 | Region 6
Mill Creek (Modoc County)

Pollutant: | Specific Conductance
Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)(2010)
Revision Status | Original
Impairment from Pollutant or Pollution: | Pollutant
Regional Board Staff Conclusion: | Regional Board Conclusion: This pollutant was considered for placement on the section 303(d) list in a previous assessment cycle. No new information was reviewed for this current assessment cycle. Therefore, the previous conclusion remains unchanged, and is as follows: This pollutant is being considered for placement on the section 303(d) list under section 3.2 of the Listing Policy. Under section 3.2 a single line of evidence is necessary to assess listing status. One line of evidence is available in the administrative record to assess this pollutant. None of the samples exceed the water quality objective. Based on the readily available data and information, the weight of evidence indicates that there is sufficient justification against placing this water segment-pollutant combination on the section 303(d) list in the Water Quality Limited Segments category. This conclusion is based on the staff findings that: 1. The data used satisfy the data quality requirements of section 6.1.4 of the Policy. 2. The data used do not satisfy the data quantity requirements of section 6.1.5 of the Policy. Quarterly samples do not capture the seasonal and annual variability expected in streamflows and dissolved ion concentrations in streams of the Lahontan Region. 3. None of 14 samples exceeded the objective and this does not exceed the allowable frequency listed in Table 3.2 of the Listing Policy. 4. Pursuant to section 3.11 of the Listing Policy, no additional data and information are available indicating that standards are not met.
Regional Board Staff Decision Recommendation: | No new data were assessed for this assessment cycle. The conclusion reached in the previous cycle remains in same. The Regional Board will update this decision when new data and information become available in a future assessment cycle.

Line of Evidence (LOE) for Decision ID 21059, Specific Conductance | Region 6
Mill Creek (Modoc County)
LOE ID: | 4845
Pollutant: | Specific Conductance
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | None
Beneficial Use: | Municipal & Domestic Supply
Number of Samples: | 14
Number of Exceedances: | 0
Data and Information Type: | Non-fixed station physical/chemical monitoring (conventional pollutant only)
Data Used to Assess Water Quality: | The U.S. Geological Survey measured specific conductance in Mill Creek under Region 6's SWAMP program. Fourteen field measurements of specific conductance ranged from 84 to 119 uS/cm. One laboratory measurement was 119 uS/cm. The objective was not exceeded.
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | California Maximum Contaminant Levels (MCLs) apply to ambient waters under the Lahontan Basin Plan's "Chemical Constituents" objective. The MCL for specific conductance is 900 microsiemens/centimeter (uS/cm).
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | Fourteen field measurements and one laboratory measurement were taken over a 4 year period between 2001 and 2005, with 2-4 sampling runs per year.
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest. Specific conductance in the lower reach of Mill Creek may be affected by windblown salts from the dry lake bed.
QAPP Information: | The data meet the quality assurance requirements of the SWAMP QAPP.
QAPP Information Reference(s):

DECISION ID | 20781 | Region 6
Mill Creek (Modoc County)

Pollutant: | Temperature, water
Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)(2010)
Revision Status | Original
Impairment from Pollutant or Pollution: | Pollutant
Regional Board Staff Conclusion: | Regional Board Conclusion: This pollutant was considered for placement on the section 303(d) list in a previous assessment cycle. No new information was reviewed for this current assessment cycle. Therefore, the previous conclusion remains unchanged, and is as follows: The Lahontan Basin Plan's narrative temperature objective is an antidegradation-based objective that requires that there be no change in temperature in waters designated for the Cold Freshwater Habitat (COLD) beneficial use. The objective does not include specific numerical limits for protection of the COLD use. Listing Policy Section 3.10 contains directions for assessment based on trends in water quality. These directions include requirements to establish specific baseline conditions and specify the influence of seasonal and interannual effects. One line of evidence is available to support this decision. There are not enough temperature samples to establish baseline conditions (including diel, seasonal, annual and interannual variations in temperature) or to detect declining trends in the temperature regime if such trends exist. Because temperature samples were collected only quarterly, weekly and monthly average data are not available for comparison with guidelines in the scientific literature for the temperature requirements of sensitive aquatic species such as salmonids, as directed in Listing Policy Section 6.1.5.9.
Regional Board Staff Decision Recommendation: | No new data were assessed for this assessment cycle. The conclusion reached in the previous cycle remains in same. The Regional Board will update this decision when new data and information become available in a future assessment cycle.

Line of Evidence (LOE) for Decision ID 20781, Temperature, water | Region 6
Mill Creek (Modoc County)
LOE ID: | 4852
Pollutant: | Temperature, water
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | None
Beneficial Use: | Cold Freshwater Habitat
Number of Samples: | 14
Number of Exceedances: | 0
Data and Information Type: | Non-fixed station physical/chemical monitoring (conventional pollutant only)
Data Used to Assess Water Quality: | The U.S. Geological Survey measured water temperature in Mill Creek under Region 6's SWAMP program. Fourteen field measurements ranged from 0 to 14.5 degrees Celsius. sampling frequency was insufficient to define natural conditions (including diel, seasonal and annual variation) or to detect whether changes have occurred.
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | The applicable language from the Lahontan Basin Plan's temperature objective is: "The natural receiving water temperature of all waters shall not be altered unless it can be demonstrated to the satisfaction fo the Regional Board that such an alteration in temperature does not adversely affect the water for beneficial uses. For waters designated WARM, water temperature shall not be altered by more than five degrees Fahrenheit (5o F) above or below the natural temperature. For waters designated COLD, the temperature shall not be altered."
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | Fourteen measurements of water temperature were taken over five years (2-4 measurements per year between 2001 and 2005). Sampling frequency was insufficient to define natural conditions (including diel, seasonal and annual variation) or to detect whether changes have occurred.
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest.
QAPP Information: | The data meet the quality assurance requirements of the SWAMP QAPP.
QAPP Information Reference(s):

DECISION ID | 21752 | Region 6
Mill Creek (Modoc County)

Pollutant: | Total Kjeldahl Nitrogen (TKN)
Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)(2010)
Revision Status | Original
Impairment from Pollutant or Pollution: | Pollutant
Regional Board Staff Conclusion: | Regional Board Conclusion: This pollutant was considered for placement on the section 303(d) list in a previous assessment cycle. No new information was reviewed for this current assessment cycle. Therefore, the previous conclusion remains unchanged, and is as follows: This pollutant is being considered for placement on the section 303(d) list under section 3.1 of the Listing Policy. Under section 3.1 a single line of evidence is necessary to assess listing status. One line of evidence is available in the administrative record to assess this pollutant. There is no biological evidence for assessment whether the chemical samples exceed the water quality objective for biostimulatory substances. Based on the readily available data and information, the weight of evidence indicates that there is sufficient justification against placing this water segment-pollutant combination on the section 303(d) list in the Water Quality Limited Segments category. This conclusion is based on the staff findings that: 1. The data used satisfy the data quality requirements of section 6.1.4 of the Policy. 2. The data used do not satisfy the data quantity requirements of section 6.1.5 of the Policy. Quarterly samples do not capture the seasonal and annual variability expected in streamflows and constituent concentrations in streams of the Lahontan Region. 3. There is insufficient biological evidence to show whether or not the applicable water quality objective was exceeded. 4. Pursuant to section 3.11 of the Listing Policy, no additional data and information are available indicating that standards are not met.
Regional Board Staff Decision Recommendation: | No new data were assessed for this assessment cycle. The conclusion reached in the previous cycle remains in same. The Regional Board will update this decision when new data and information become available in a future assessment cycle.

Line of Evidence (LOE) for Decision ID 21752, Total Kjeldahl Nitrogen (TKN) | Region 6
Mill Creek (Modoc County)
LOE ID: | 5813
Pollutant: | Total Kjeldahl Nitrogen (TKN)
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | Dissolved
Beneficial Use: | Cold Freshwater Habitat
Number of Samples: | 10
Number of Exceedances: | 0
Data and Information Type: | Fixed station physical/chemical (conventional plus toxic pollutants)
Data Used to Assess Water Quality: | The U.S. Geological Survey sampled Mill Creek under the Region 6 SWAMP program. Ten quarterly samples were collected between 2002 and 2005 (1 to 4 samples/year). TKN concentrations ranged from 0.05 to 0.24 mg/L. No data on algae or macrophytes are available for assessment of compliance with the water quality objective for biostimulatory substances.
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | The Lahontan Basin Plan does not include a site-specific objective for Total Kjeldahl Nitrogen (TKN) for Mill Creek. A separate line of evidence has been prepared for the Total Nitrogen objective in Basin Plan Table 3-7. The narrative objective for biostimulatory substances states: "Waters shall not contain biostimulatory substances in concentrations that promote aquatic growths to the extent that such growths cause nuisance or adversely affect the water for beneficial uses."
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | Ten samples were collected at quarterly intervals between 2002 and 2005, with 1 to 4 samples per year.
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest. Chloride concentrations in the lower reach of the creek may be influenced by windblown salts from the dry lake bed.
QAPP Information: | The data meet the quality assurance requirements of the SWAMP QAPP.
QAPP Information Reference(s):

DECISION ID | 21092 | Region 6
Mill Creek (Modoc County)

Pollutant: | Total Nitrogen as N
Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)(2010)
Revision Status | Original
Impairment from Pollutant or Pollution: | Pollutant
Regional Board Staff Conclusion: | Regional Board Conclusion: This pollutant was considered for placement on the section 303(d) list in a previous assessment cycle. No new information was reviewed for this current assessment cycle. Therefore, the previous conclusion remains unchanged, and is as follows: This pollutant is being considered for placement on the section 303(d) list under section 3.1 of the Listing Policy. Under section 3.1 a single line of evidence is necessary to assess listing status. One line of evidence is available in the administrative record to assess this pollutant. None of the samples (annual average datapoints) exceed the water quality objective. Based on the readily available data and information, the weight of evidence indicates that there is sufficient justification against placing this water segment-pollutant combination on the section 303(d) list in the Water Quality Limited Segments category. This conclusion is based on the staff findings that: 1. The data used satisfy the data quality requirements of section 6.1.4 of the Policy. 2. The data used do not satisfy the data quantity requirements of section 6.1.5 of the Policy. Quarterly samples do not capture the seasonal and annual variability expected in streamflows and constituent concentrations in streams of the Lahontan Region. 3. None of five annual average datapoints exceeded the site specific water quality objective and this does not exceed the allowable frequency listed in Table 3.1 of the Listing Policy. 4. Pursuant to section 3.11 of the Listing Policy, no additional data and information are available indicating that standards are not met.
Regional Board Staff Decision Recommendation: | No new data were assessed for this assessment cycle. The conclusion reached in the previous cycle remains in same. The Regional Board will update this decision when new data and information become available in a future assessment cycle.

Line of Evidence (LOE) for Decision ID 21092, Total Nitrogen as N | Region 6
Mill Creek (Modoc County)
LOE ID: | 5811
Pollutant: | Total Nitrogen as N
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | Total
Beneficial Use: | Cold Freshwater Habitat
Number of Samples: | 5
Number of Exceedances: | 0
Data and Information Type: | Fixed station physical/chemical (conventional plus toxic pollutants)
Data Used to Assess Water Quality: | The U.S. Geological Survey sampled Mill Creek under the Region 6 SWAMP program. Ten quarterly samples were collected between 2001 and 2005 (1 to 4 samples/year). Single sample concentrations of Total N ranged from 0.061 to 0.265 mg/L. The annual average objective was not violated.
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | The site-specific objective for Total Nitrogen in Lahontan Basin Plan Table 3-7 is 0.2 mg/L as an annual average.
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | Ten samples were collected at approximately quarterly intervals between 2001 and 2005, with 1 to 4 samples per year.
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest. Chloride concentrations in the lower reach of the creek may be influenced by windblown salts from the dry lake bed.
QAPP Information: | The data meet the quality assurance requirements of the SWAMP QAPP.
QAPP Information Reference(s):

DECISION ID | 21740 | Region 6
Mill Creek (Modoc County)

Pollutant: | Turbidity
Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)(2010)
Revision Status | Original
Impairment from Pollutant or Pollution: | Pollutant
Regional Board Staff Conclusion: | Regional Board Conclusion: This pollutant was considered for placement on the section 303(d) list in a previous listing cycle. No new information was reviewed for this current assessment cycle. Therefore, the previous conclusion remains unchanged, and is as follows: This pollutant is being considered for placement on the section 303(d) list under section 3.2 of the Listing Policy. Under section 3.2 a single line of evidence is necessary to assess listing status. Two lines of evidence are available in the administrative record to assess this pollutant. The single sample did not exceed the Maximum Contaminant Level. The Lahontan Basin Plan's narrative objective for turbidity is antidegradation based. The single sample does not allow establishment of background conditions or documentation of trends to determine compliance with the water quality objective under Listing Policy Section 3.10. Based on the readily available data and information, the weight of evidence indicates that there is sufficient justification against placing this water segment-pollutant combination on the section 303(d) list in the Water Quality Limited Segments category. This conclusion is based on the staff findings that: 1. No quality assurance information is available to show whether the sample used satisfies the data quality requirements of section 6.1.4 of the Policy. 2. The single sample used does not satisfy the data quantity requirements of section 6.1.5 of the Policy. 3. The single sample used did not exceed either of the applicable water quality objectives, and this does not exceed the allowable frequency listed in Table 3.2 of the Listing Policy. 4. Pursuant to section 3.11 of the Listing Policy, no additional data and information are available indicating that standards are not met.
Regional Board Staff Decision Recommendation: | No new data were assessed for this assessment cycle. The conclusion reached in the previous cycle remains the same. The Regional Board will update this decision when new data and information become available in a future assessment cycle.

Line of Evidence (LOE) for Decision ID 21740, Turbidity | Region 6
Mill Creek (Modoc County)
LOE ID: | 4850
Pollutant: | Turbidity
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | None
Beneficial Use: | Municipal & Domestic Supply
Number of Samples: | 11
Number of Exceedances: | 2
Data and Information Type: | Fixed station physical/chemical (conventional plus toxic pollutants)
Data Used to Assess Water Quality: | The U.S. Geological Survey measured turbidity in Mill Creek under Region 6's SWAMP program. Eleven turbidity measurements expressed as NTU ranged from below the detection level to 12 NTU (two samples were below the detection level). Two samples exceeded the MCL.
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | Drinking water Maximum Contaminant Levels (MCLs) apply to ambient waters under the Lahontan Basin Plan's Chemical Constituents objective. The MCL for turbidity is 5 Nepehelometric Turbidity Units (NTU).
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | Eleven turbidity measurements expressed as NTU were taken between 2001 and 2004.
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest.
QAPP Information: | The data meet the quality assurance requirements of the SWAMP QAPP.
QAPP Information Reference(s):
Line of Evidence (LOE) for Decision ID 21740, Turbidity | Region 6
Mill Creek (Modoc County)
LOE ID: | 4849
Pollutant: | Turbidity
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | None
Beneficial Use: | Cold Freshwater Habitat
Number of Samples: | 11
Number of Exceedances: | 0
Data and Information Type: | Fixed station physical/chemical (conventional plus toxic pollutants)
Data Used to Assess Water Quality: | The U.S. Geological Survey measured turbidity in Mill Creek under Region 6's SWAMP program. Two of 11 turbidity measurements expressed as NTU were below the detection level. Turbidity in the remainder of the samples ranged 0.6 to 12 NTU. Sampling frequency was insufficient to define natural conditions, assess whether changes have occurred, or assess effects on beneficial uses.
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | The applicable narrative objective from the Lahontan Basin Plan states: "Waters shall be free of changes in turbidity that cause nuisance or adversely affect the water for beneficial uses. Increases in turbidity shall not exceed natural levels by more than 10 percent."
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | Eleven turbidity measurements expressed as NTU were taken between 2001 to 2004. Sampling frequency was insufficient to define natural conditions, assess whether changes have occurred, or assess effects on beneficial uses
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest.
QAPP Information: | The data meet the quality assurance requirements of the SWAMP QAPP.
QAPP Information Reference(s):
Line of Evidence (LOE) for Decision ID 21740, Turbidity | Region 6
Mill Creek (Modoc County)
LOE ID: | 7483
Pollutant: | Turbidity
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | None
Beneficial Use: | Cold Freshwater Habitat
Number of Samples: | 3
Number of Exceedances: | 0
Data and Information Type: | Fixed station physical/chemical (conventional plus toxic pollutants)
Data Used to Assess Water Quality: | The U.S. Geological Survey measured turbidity in Mill Creek under Region 6's SWAMP program. Two of 3 turbidity measurements expressed as NTRU were below the detection level. Turbidity in the remaining sample was 3.8 NTRU. Sampling frequency was insufficient to define natural conditions, assess whether changes have occurred, or assess effects on beneficial uses.
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | The applicable narrative objective from the Lahontan Basin Plan states: "Waters shall be free of changes in turbidity that cause nuisance or adversely affect the water for beneficial uses. Increases in turbidity shall not exceed natural levels by more than 10 percent."
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | Three turbidity measurements expressed as NTRU were taken in 2003 and 2004. Sampling frequency was insufficient to define natural conditions, assess whether changes have occurred, or assess effects on beneficial uses
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest.
QAPP Information: | The data meet the quality assurance requirements of the SWAMP QAPP.
QAPP Information Reference(s):
Line of Evidence (LOE) for Decision ID 21740, Turbidity | Region 6
Mill Creek (Modoc County)
LOE ID: | 7485
Pollutant: | Turbidity
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | None
Beneficial Use: | Municipal & Domestic Supply
Number of Samples: | 3
Number of Exceedances: | 0
Data and Information Type: | Fixed station physical/chemical (conventional plus toxic pollutants)
Data Used to Assess Water Quality: | The U.S. Geological Survey measured turbidity in Mill Creek under Region 6's SWAMP program. Three turbidity measurements expressed as NTRU were taken in 2004 and 2005. Two of the results were below the detection level; turbidity in the remaining sample was 3.8 NTRU.
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | Drinking water Maximum Contaminant Levels (MCLs) apply to ambient waters under the Lahontan Basin Plan's Chemical Constituents objective. The MCL for turbidity is 5 Nepehelometric Turbidity Units (NTU). There is no MCL for turbidity expressed as NTRU.
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | Three turbidity measurements expressed as NTRU were taken between 2004 and 2005
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest.
QAPP Information: | The data meet the quality assurance requirements of the SWAMP QAPP.
QAPP Information Reference(s):

DECISION ID | 21996 | Region 6
Mill Creek (Modoc County)

Pollutant: | pH
Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision: | Do Not List on 303(d) list (TMDL required list)(2010)
Revision Status | Original
Impairment from Pollutant or Pollution: | Pollutant
Regional Board Staff Conclusion: | Regional Board Conclusion: This pollutant was considered for placement on the section 303(d) list in a previous assessment cycle. No new information was reviewed for this current assessment cycle. Therefore, the previous conclusion remains unchanged, and is as follows: The Lahontan Basin Plan's narrative pH objective is an antidegradation-based objective that requires that there be no change greater than 0.5 pH units in waters designated for the Cold Freshwater Habitat (COLD) or Warm Freshwater Habitat beneficial uses. Listing Policy Section 3.10 contains directions for assessment based on trends in water quality. These directions include requirements to establish specific baseline conditions and specify the influence of seasonal and interannual effects. Two lines of evidence are available to support this decision. There are not enough pH samples to establish baseline conditions (including diel, seasonal, annual and interannual variations) or to detect changes in the pH regime due to controllable factors, if such trends exist.
Regional Board Staff Decision Recommendation: | No new data were assessed for this assessment cycle. The conclusion reached in the previous cycle remains in same. The Regional Board will update this decision when new data and information become available in a future assessment cycle.

Line of Evidence (LOE) for Decision ID 21996, pH | Region 6
Mill Creek (Modoc County)
LOE ID: | 4842
Pollutant: | pH
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | None
Beneficial Use: | Cold Freshwater Habitat
Number of Samples: | 14
Number of Exceedances: | 0
Data and Information Type: | Fixed station physical/chemical (conventional plus toxic pollutants)
Data Used to Assess Water Quality: | The U.S. Geological Survey measured pH for Mill Creek under the Region 6 SWAMP program. There were no violations of the 6.5 to 8.5 units limits in 14 field samples and one laboratory sample. The pH ranged from 6.7 to 8.4 units. There are insufficient data available to characterize normal ambient pH levels and evaluate compliance with the 0.5 unit limit on pH changes.
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | The Lahontan Basin Plan's objective for pH states: "In fresh waters with designated beneficial uses of COLD or WARM, changes in normal ambient pH levels shall not exceed 0.5 pH units. For all other waters of the region, the pH shall not be depressed below 6.5 nor raised above 8.5 units. The Regional Board recognizes that some waters of the Region may have natural pH levels outside of the 6.5 to 8.5 range. Compliance with the pH objective for these waters will be determined on a case-by-case basis."
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | Fourteen field measurements and one laboratory measurement of pH were taken over a five year period (from 2001 to 2005), with 2-4 samples per year. Sampling frequency was too low to characterize the normal pH regime or allow detection of changes.
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest. In addition to the Cold Freshwater Habitat beneficial use, Mill Creek is designated for the Spawning, Reproduction and Development use.
QAPP Information: | The data meet the quality assurance requirements of the SWAMP QAPP.
QAPP Information Reference(s):
Line of Evidence (LOE) for Decision ID 21996, pH | Region 6
Mill Creek (Modoc County)
LOE ID: | 4843
Pollutant: | pH
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | None
Beneficial Use: | Municipal & Domestic Supply
Number of Samples: | 14
Number of Exceedances: | 0
Data and Information Type: | Fixed station physical/chemical (conventional plus toxic pollutants)
Data Used to Assess Water Quality: | The U.S. Geological Survey measured pH for Mill Creek under the Region 6 SWAMP program. There were no violations of the 6.5 to 8.5 units limits in 14 field samples and one lab sample. The pH ranged from 6.7 to 8.4 units. There are insufficient data available to characterize normal ambient pH levels and evaluate compliance with the 0.5 unit limit on pH changes.
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | The Lahontan Basin Plan's objective for pH states: "In fresh waters with designated beneficial uses of COLD or WARM, changes in normal ambient pH levels shall not exceed 0.5 pH units. For all other waters of the region, the pH shall not be depressed below 6.5 nor raised above 8.5 units. The Regional Board recognizes that some waters of the Region may have natural pH levels outside of the 6.5 to 8.5 range. Compliance with the pH objective for these waters will be determined on a case-by-case basis."
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | Fourteen field measurements and one laboratory measurement of pH were taken over a five year period (from 2001 to 2005), with 2-4 samples per year. Sampling frequency was too low to characterize the normal pH regime or allow detection of changes.
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest.
QAPP Information: | The data meet the quality assurance requirements of the SWAMP QAPP.
QAPP Information Reference(s):

DECISION ID | 28408 | Region 6
Mill Creek (Modoc County)

Pollutant: | Total Dissolved Solids
Final Listing Decision: | List on 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision: | List on 303(d) list (TMDL required list)(2010)
Revision Status | Original
Sources: | Source Unknown
Expected TMDL Completion Date: | 2021
Impairment from Pollutant or Pollution: | Pollutant
Regional Board Staff Conclusion: | Regional Board Conclusion: This pollutant was considered for placement on the section 303(d) list in a previous assessment cycle. No new information was reviewed for this current assessment cycle. Therefore, the previous conclusion remains unchanged, and is as follows: Regional Board Conclusion: This pollutant is being considered for placement on the section 303(d) list under section 3.2 of the Listing Policy. Under section 3.2 a single line of evidence is necessary to assess listing status. Two lines of evidence are available in the administrative record to assess this pollutant. Five of the annual average datapoints exceed the water quality objective. However, listing is not recommended because the data are not temporally representative. Based on the readily available data and information, the weight of evidence indicates that there is sufficient justification against placing this water segment-pollutant combination on the section 303(d) list in the Water Quality Limited Segments category. This conclusion is based on the staff findings that: 1. The data used satisfy the data quality requirements of section 6.1.4 of the Policy. 2. The data used do not satisfy the data quantity requirements of section 6.1.5 of the Policy. Quarterly (or less frequent) samples do not capture the full range of seasonal and annual variability expected in streamflows and constituent concentrations in streams of the Lahontan Region. 3. Five of five annual average datapoints and this exceeds the allowable frequency listed in Table 3.2 of the Listing Policy. 4. Pursuant to section 3.11 of the Listing Policy, no additional data and information are available indicating that standards are not met. State Board Review and Conclusion: The April 19, 2010 State Water Board staff report for the 2010 Integrated Report recommended to place this water body on the 303(d) list for total dissolved solids based on the State Water Board staff determination that the data were collected over a broad period of time to meet section 6.1.5.3 of the Listing Policy. The State Water Board recommendation is based on the following: Lahontan Regional Board staff had decided not to list this water body because staff thought it had insufficient information to make a decision to list. However, State Board staff finds there are five samples to make a decision and this meets the sample size requirements of Table 3.2 of the Listing Policy. On August 4, 2010 the State Water Board approved the staff recommendation to place this water body-pollutant combination on the 303(d) list. The final language for the recommendation is: Based on the readily available data and information, the weight of evidence indicates that there is sufficient justification in favor of placing this water segment-pollutant combination on the section 303(d) list in the Water Quality Limited Segments category. This conclusion is based on the staff findings that: 1. The data used satisfy the data quality requirements of section 6.1.4 of the Policy. 2. The data used satisfy the data quantity requirements of section 6.1.5 of the Policy. 3. Five of five annual average datapoints and this exceeds the allowable frequency listed in Table 3.2 of the Listing Policy. 4. Pursuant to section 3.11 of the Listing Policy, no additional data and information are available indicating that standards are not met.
Regional Board Staff Decision Recommendation: | No new data were assessed for this assessment cycle. The conclusion reached in the previous cycle remains in same. The Regional Board will update this decision when new data and information become available in a future assessment cycle.

Line of Evidence (LOE) for Decision ID 28408, Total Dissolved Solids | Region 6
Mill Creek (Modoc County)
LOE ID: | 4847
Pollutant: | Total Dissolved Solids
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | Total Dissolved
Beneficial Use: | Cold Freshwater Habitat
Number of Samples: | 5
Number of Exceedances: | 5
Data and Information Type: | Fixed station physical/chemical (conventional plus toxic pollutants)
Data Used to Assess Water Quality: | The U.S. Geological Survey sampled TDS in Mill Creek under Region 6's SWAMP program. Single sample concentrations ranged from 69 to 96 mg/L; only one sample was below 70 mg/L. Annual average concentrations exceeded the objective in 5 of 5 years.
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | The site specific objective for Total Dissolved Solids is 70 mg/L as an annual average (Lahontan Basin Plan Table 3-7).
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | Fourteen samples were collected over 5 years (2 to 4 samples/year, between 2001 to 2005).
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest. TDS concentrations in the lower reach of Mill Creek may be influenced by windblown salts from the dry lake bed.
QAPP Information: | The data meet the quality assurance requirements of the SWAMP QAPP.
QAPP Information Reference(s):
Line of Evidence (LOE) for Decision ID 28408, Total Dissolved Solids | Region 6
Mill Creek (Modoc County)
LOE ID: | 4848
Pollutant: | Total Dissolved Solids
LOE Subgroup: | Pollutant-Water
Matrix: | Water
Fraction: | Total Dissolved
Beneficial Use: | Municipal & Domestic Supply
Number of Samples: | 14
Number of Exceedances: | 0
Data and Information Type: | Fixed station physical/chemical (conventional plus toxic pollutants)
Data Used to Assess Water Quality: | The U.S. Geological Survey sampled TDS in Mill Creek under Region 6's SWAMP program. TDS concentrations in 14 samples ranged from 69 to 96 mg/L. The MCL was not exceeded.
Data Reference: | 2007. SWAMP Data for Waters of the Surprise Valley Hydrologic Unit
SWAMP Data: | SWAMP
Water Quality Objective/Criterion: | California Maximum Contaminant Levels (MCLs) apply to ambient waters under the Lahontan Basin Plan's "Chemical Constituents" objective. The MCL for Total Dissolved Solids (TDS) is 500 mg/L.
Objective/Criterion Reference: | Water Quality Control Plan for the Lahontan Region (as amended)
Evaluation Guideline: |
Guideline Reference:
Spatial Representation: | One station, Mill Creek at Upper Lake near Lake City, was sampled.
Temporal Representation: | Fourteen samples were collected over 5 years (2- 4 samples/year, between 2001 to 2005).
Environmental Conditions: | Mill Creek (Modoc County) is tributary to Upper Alkali Lake, an ephemeral desert playa lake in Surprise Valley. (This Mill Creek should not be confused with the Mill Creek tributary to Bidwell Creek in the same watershed.) Most of the watershed is in Modoc National Forest. TDS concentrations in the lower reach of Mill Creek may be influenced by windblown salts from the dry lake bed.
QAPP Information: | The data meet the quality assurance requirements of the SWAMP QAPP.
QAPP Information Reference(s):